Dual-inverter for a brushless motor

ABSTRACT

A power tool is provided including: an electric brushless direct current (BLDC) motor having rotor and a stator defining phases; a power unit including a first switch circuit connected electrically between a first power supply and the motor, and a second switch circuit connected electrically between a second power supply and the motor; and a controller configured to control a switching operation of the first switch circuit and the second switch circuit to regulate a supply of power from at least one of the first power supply and/or the second power supply to the motor.

RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application No.62/385,433 filed Sep. 9, 2016, content of which is incorporated hereinby reference in its entirety.

FIELD

This disclosure relates to brushless motor controls. More particularly,the present invention relates to a dual-inverter circuit for a brushlessmotor.

BACKGROUND

Power tools may be of different types depending on the type of outputprovided by the power tool. Power tools such as drills, hammers,grinders, impact wrenches, circular saws, reciprocating saws, and so onare marketed in different parts of the world and used widely inconsumer, DIY, and construction market. Power tools may be provided witha rotary motor such as a brushless DC (BLDC) motor.

Conventionally, large power tools that require high power for heavy dutyapplications may be powered by an alternating current (AC) power source,while other portable power tools may be powered by a direct current (DC)power source such as a battery pack. More recently, power tools thatwere conventionally powered by AC power sources only have been providedwith the capability to receive AC or DC power supplies. U.S. Pat. No.9,406,915, filed May 18, 2015, which incorporated herein by reference inits entirety, provides examples of AC/DC power tools that can be poweredby an AC power supply, a DC power supply, or a hybrid combination of ACand DC power supplies.

Power tools including BLDC motors typically include an inverter circuitincluding a series of semiconductor solid-state switches that drive thedifferent phases of the motor. The type of switches employed in suchcircuits are selected based on the power output requirements.

BLDC motors may also be wound differently based on the power outputrequirements. The two basic winding configurations for the phases of themotor are wye and delta connections. A motor with windings configured inthe delta configuration can operate at a greater speed than the samewindings configured in the wye configuration. A motor with windingsconfigured in the wye configuration can operate with a greater torquethan the same windings configured in the delta configuration.

Furthermore, the windings within each phase of the motor may beconnected in either series or parallel. A series connection is oftenmore suitable for relatively high voltage applications, and a parallelconnection is often more suitable for relatively low voltageapplications.

What is needed is a system that can utilize proper inverter switches forthe needed application without sacrificing performance. What is furtherneeded is a system that can configure the motor in the most effectivemanner based on the power requirements of the power tool to increasemotor efficiency.

The background description provided here is for the purpose of generallypresenting the context of the disclosure. Work of the presently namedinventors, to the extent it is described in this background section, aswell as aspects of the description that may not otherwise qualify asprior art at the time of filing, are neither expressly nor impliedlyadmitted as prior art against the present disclosure.

SUMMARY

According to an embodiment of the invention, a power tool is providedincluding: an electric brushless direct current (BLDC) motor havingrotor and a stator defining phases; a power unit including a firstswitch circuit connected electrically between a first power supply andthe motor, and a second switch circuit connected electrically between asecond power supply and the motor; and a controller configured tocontrol a switching operation of the first switch circuit and the secondswitch circuit to regulate a supply of power from at least one of thefirst power supply and/or the second power supply to the motor.

In an embodiment, the first power supply is an alternating current (AC)power supply coupled to a bridge rectifier to generate a positivevoltage waveform, and the second power supply is a direct current (DC)power supply.

In an embodiment, the first switch circuit includes insulated-gatebipolar transistors (IGBTs) and the second switch circuit includesfield-effect transistors (FETs).

In an embodiment, the stator defines three phases with each phasecorresponding to two windings electrically connected. In an embodiment,each of the first switch circuit and the second switch circuit isconfigured as a three-phase inverter circuit. In an embodiment, eachphase is electrically coupled to both the first switch circuit and thesecond switch circuit and is selectively driven by one of the firstswitch circuit or the second switch circuit.

In an embodiment, the stator defines six phases with each phasecorresponding to a winding, a first set of windings being coupled to thefirst switch circuit and a second set of windings being coupled tosecond switch circuit. In an embodiment, the first set of windings andthe second set of windings are alternatingly distributed around thestator. In an embodiment, the first set of windings includes thickermagnet wires wound at a lower number of turns than the second set ofwindings.

In an embodiment, the first and the second power supplies drive themotor in tandem. In an embodiment, the first power supply is analternating current (AC) power supply, the second power supply is adirect current (DC) power supply, and a current draw by the motorexceeds an average current provided by the first power supply. In anembodiment, the controller is configured to enable current draw from thesecond power supply when the current draw by the motor exceeds athreshold. In an embodiment, the controller is configured to enablecurrent draw from the second power supply for predetermined time periodsbefore and after zero-crossings of the first power supply voltage.

In an embodiment, the power tool further includes a charging circuitarranged to charge the second power supply from the power supplied viathe first power supply. In an embodiment, the charging circuit isarranged between one or more drive signals of the first switch circuitand the second power supply.

In an embodiment, the power tool further includes a power supplyregulator coupled to the first power supply and the second power supplyto generate a voltage signal for powering the controller.

According to another aspect/embodiment of the invention, a power tool isprovided including: an electric brushless direct current (BLDC) motorhaving a rotor and a stator defining phases; a power unit including afirst switch circuit connected electrically between a first power supplyand the motor, and a second switch circuit connected electricallybetween a second power supply and the motor, to effectively provide aparallel connection between the first power supply and the second powersupply; and a controller configured to control a switching operation ofthe first switch circuit and the second switch circuit to regulate asupply of power from the first power supply and the second power supplyto the motor.

In an embodiment, the first power supply and the second power supply areboth direct current (DC) power supplies.

In an embodiment, the first switch circuit and the second switch circuitboth include insulated-gate bipolar transistors (IGBTs). Alternatively,in an embodiment, the first switch circuit and the second switch circuitboth include field-effect transistors (FETs).

In an embodiment, the first switch circuit and the second switch circuitare arranged to electrically isolate the first power supply from thesecond power supply to prevent flow of current from first power supplyto the second power supply or vice versa.

In an embodiment, the controller is configured to control motorcommutation by concurrently driving the first switch circuit and thesecond switch circuit using one set of drive signals.

In an embodiment, the stator includes a series of windings associatedwith the phases, first switch circuit is electrically connected to afirst set of stator windings, and the second switch circuit iselectrically connected to a second set of stator windings. In anembodiment, the first set of windings and the second set of windings arealternatingly disposed around the stator.

In an embodiment, the power tool further includes a battery selectorswitch disposed between the first power supply and the second switchcircuit to selectively couple the first power supply to the secondswitch circuit when the second power supply is not present.

According to an alternative embodiment, a power tool is providedincluding an electric brushless direct current (BLDC) motor having arotor and a stator defining phases associated with windings; a powerunit including a first switch circuit connected electrically between afirst power supply and a first set of stator windings and a secondswitch circuit connected electrically between a second power supply anda second set of windings; and a controller configured to control aswitching operation of the first switch circuit and the second switchcircuit to regulate a supply of power from the first power supply andthe second power supply to the motor. In an embodiment, the power uniteffectively provides a parallel connection between the first powersupply and the second power supply.

According to another aspect/embodiment of the invention, a power tool isprovided including an electric brushless direct current (BLDC) motorhaving a rotor and a stator defining phases associated with windings. Apower unit is electrically connected between a power supply and themotor, the power unit including a first switch circuit connectedelectrically to a first set of stator windings and a second switchcircuit connected electrically to a second set of windings. The firstswitch circuit and the second switch circuit are arranged to facilitateone of a series or a parallel connection between corresponding windingsof the first and second sets of stator windings. A controller isprovided and configured to control a switching operation of the firstswitch circuit and the second switch circuit to regulate a supply ofpower from the power supply to the motor.

In an embodiment, the power supply is a direct current (DC) powersupply.

In an embodiment, the power supply is defines as an alternating-current(AC) power supply and a bridge rectifier arranged to generate a positivevoltage waveform from the AC power supply. In an embodiment, the powertool further includes a capacitor coupled to the rectifier.

In an embodiment, the first switch circuit and the second switch circuitboth include insulated-gate bipolar transistors (IGBTs) or field-effecttransistors (FETs).

In an embodiment, the first switch circuit and the second switch circuiteach includes a positive terminal and a negative terminal.

In an embodiment, the positive terminals of the first and second switchcircuits are commonly coupled to a positive terminal of the powersupply, and the negative terminals of the first and second switchcircuits are commonly coupled to a negative terminal of the powersupply, to effectively create a parallel connection betweencorresponding windings of the first and second sets of stator windings.

Alternatively, in an embodiment, the positive terminal of the firstswitch circuit and the negative terminal of the second switch circuitare electrically coupled to the power supply, and the negative terminalof the first switch circuit is electrically coupled to the positiveterminal of the second switch circuit, to effectively create a seriesconnection between corresponding windings of the first and second setsof stator windings.

In an embodiment, the first switch circuit and the second switch circuiteach includes power switches having a voltage rating that isapproximately half a nominal voltage of the power supply.

In an embodiment, the power tool further includes a switching unitdisposed between two or more of the positive and negative terminals ofthe first and second switch circuits to selectively connect the firstswitch circuit and the second switch circuit in a way to facilitate oneof a series or a parallel connection between corresponding windings ofthe first and second sets of stator windings. In an embodiment, theswitching unit selectively couples the negative terminal of the firstswitch circuit to one of the positive terminal of the second switchcircuit or the negative terminal of the second switch circuit. In anembodiment, the switching unit comprises two single-pole double-throwswitches.

In an embodiment, the corresponding windings of the first and secondsets of stator windings are not electrically connected via an electricalconnection on the stator.

In an embodiment, the controller is configured to control motorcommutation by concurrently driving the first switch circuit and thesecond switch circuit using one set of drive signals.

According to another aspect/embodiment of the invention, a power tool isprovided including: an electric brushless direct current (BLDC) motorhaving a rotor and a stator defining phases associated with windings; apower unit electrically connected between a power supply and the motor,the power unit including a first switch circuit connected electricallyto a first set of stator windings and a second switch circuit connectedelectrically to a second set of windings; and a controller configured tocontrol a switching operation of the first switch circuit and the secondswitch circuit to regulate a supply of power from the power supply tothe motor. In an embodiment, the first set of stator windings areconnected together in a first winding configuration and the second setof stator windings are connected together in a second windingconfiguration that is different from the first winding configuration.

In an embodiment, the first winding configuration is a wye configurationand the second winding configuration is a delta configuration.

In an embodiment, the controller is configured to drive the first switchcircuit and the second switch circuit using a six-phase commutationsequence. In an embodiment, drive signals for the first switch signalare advanced by a lead angle compared to drive signals for the secondswitch circuit. In an embodiment, the lead angle is approximately 30degrees.

In an embodiment, the phase current corresponding to the first set ofstator windings and the phase current corresponding to the second set ofstator windings are in line with a back-electromagnetic force (back-EMF)voltage of the motor.

In an embodiment, the motor line current corresponding to the first setof stator windings is shifted by approximately the lead angle comparedto motor line current corresponding to the second set of statorwindings.

In an embodiment, the power supply is an alternating-current (AC) powersupply. In an embodiment, a bridge rectifier is arranged to generate apositive voltage waveform from the AC power supply. In an embodiment, acapacitor is further provided and coupled to an output of the bridgerectifier.

In an embodiment, the first switch circuit and the second switch circuitboth comprise a plurality of insulated-gate bipolar transistors (IGBTs)or a plurality of field-effect transistors (FETs).

In an embodiment, the first set of windings and the second set ofwindings are alternatingly distributed around the stator.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings described herein are for illustrative purposes only ofselected embodiments and not all possible implementations, and are notintended to limit the scope of the present disclosure.

FIG. 1 depicts a perspective view of a power tool, according to anembodiment;

FIG. 2 depicts a side view of the power tool with the housing partiallyremoved, according to an embodiment;

FIGS. 3 and 4 depict perspective front and rear exploded view of thepower tool, according to an embodiment;

FIGS. 5A and 5B depict perspective front and rear views of a motor andpower module employed in the power tool, according to an embodiment;

FIG. 6 depicts a perspective exploded view of the motor and powermodule, according to an embodiment;

FIG. 7 depicts a block circuit diagram of a conventional AC/DC powertool, according to an embodiment;

FIG. 8 depicts a block circuit diagram of an AC/DC power tool having adual-inverter circuit, according to an embodiment;

FIG. 9 depicts a circuit diagram of a FET switch inverter utilized inthe dual-inverter circuit, according to an embodiment;

FIG. 10 depicts a circuit diagram of an IGBT switch inverter utilized inthe dual-inverter circuit, according to an embodiment;

FIGS. 11A and 11B depict axial views of motor windings coupled to thetwo inverter circuits, according to an embodiment;

FIG. 12 depicts a comparative speed-torque diagram for three exemplarymotors that are differently wound and/or have different stator stacklengths, according to an embodiment;

FIG. 13 depicts a comparative power-torque diagram of the threeexemplary motors of FIG. 12, according to an embodiment;

FIG. 14 depicts an exemplary current diagram of the DC and AC linecurrents being supplied through the AC and DC power supplies in thehybrid mode, according to an embodiment;

FIG. 15 depicts an additional and/or improved block diagram of an AC/DCpower tool having a dual-inverter circuit, additionally provided with acharging circuit, according to an embodiment;

FIG. 16 depicts a current diagram for two battery packs having differentstates of charge, coupled in parallel at the battery receptacleterminals, according to an embodiment;

FIG. 17 depicts a block circuit diagram of a DC power tool having adual-inverter circuit, according to an embodiment;

FIG. 18 depicts a current diagram for two battery packs having differentstates of charge, coupled in parallel via the dual-inverter circuit,according to an embodiment;

FIG. 19 depicts a comparative current/torque diagram depicting currentdraw from a single battery pack v. two battery packs connected inparallel, according to an embodiment;

FIG. 20 depicts a comparative power/torque diagram depicting currentdraw from a single battery pack v. two battery packs connected inparallel, according to an embodiment;

FIG. 21 depicts a comparative speed/torque diagram depicting currentdraw from a single battery pack v. two battery packs connected inparallel, according to an embodiment;

FIG. 22 depicts a comparative efficiency/torque diagram depictingcurrent draw from a single battery pack v. two battery packs connectedin parallel, according to an embodiment;

FIGS. 23 and 24 respectively depict exemplary winding configurations fora wye-series connection and a wye-parallel connection, according to anembodiment;

FIG. 25 depicts a block circuit diagram of an AC power tool having adual-inverter circuit configured to connect the motor windings of eachphase of the motor in parallel, according to an embodiment;

FIG. 26 depicts a block circuit diagram of an AC power tool having adual-inverter circuit configured to connect the motor windings inseries, according to an embodiment;

FIG. 27 depicts a voltage waveform diagram for a conventionalthree-phase BLDC motor wound in a series connection and driven via asingle three-phase inverter circuit, according to an embodiment;

FIG. 28 depicts a voltage waveform diagram corresponding to a parallelmotor connection via a dual-inverter circuit as shown circuit diagram ofFIG. 25, according to an embodiment;

FIG. 29 depicts a block circuit diagram of an AC power tool having adual-inverter circuit, further provided with a switching unit toselectively connect the motor windings of each phase of the motor inseries or parallel, according to an embodiment;

FIG. 30 depicts an exemplary switching unit for the circuit diagram ofFIG. 29, according to an embodiment;

FIGS. 31 and 32 respectively depict comparative power output/torquediagram and AC current/torque of a motor being connected in series andparallel using the dual-inverter circuit, according to an embodiment;

FIG. 33 depicts a current diagram for a conventional three-phase BLDCmotor coupled to an AC power supply, according to an embodiment;

FIGS. 34 and 35 respectively depict exemplary wye and delta motorconfigurations, according to an embodiment;

FIG. 36 depicts a block circuit diagram of an AC power tool having adual-inverter circuit configured for operation the motor windings in sixphases, where three windings are connected in a wye configuration andthree are connected in a delta configurations, according to anembodiment;

FIG. 37 depicts three stator windings connected in a wye configuration,according to an embodiment;

FIG. 38 depicts three stator windings connected in a deltaconfiguration, according to an embodiment;

FIG. 39 depicts an exemplary waveform diagram for six-phase commutationsequence of the motor, according to an embodiment;

FIG. 40 depicts a waveform diagram showing the motor phase currents foran exemplary wye-connected phase and an exemplary delta-connected phaseof the motor, according to an embodiment;

FIG. 41 depicts a waveform diagram showing the motor line currents forthe exemplary wye-connected phase and the exemplary delta-connectedphase of the motor, according to an embodiment;

FIG. 42 depicts a waveform diagram showing another comparative view ofthe motor line current for phases A (wye connection) and D (deltaconnection), as well as the AC input current as measured from the powersupply, according to an embodiment;

FIG. 43 depicts comparative waveform diagrams of the AC input currentfor a conventional three-phase motor, and the AC input current for amotor configured and controlled according to the six-phase commutationsequence of this disclosure, according to an embodiment;

FIG. 44 depicts comparative waveform diagrams of power factor of aconventional three-phase motor, and power factor of a motor configuredand controlled according to the six-phase commutation sequence of thisdisclosure, according to an embodiment;

FIG. 45 depicts comparative waveform diagrams of power output of aconventional three-phase motor, and power output of a motor configuredand controlled according to the six-phase commutation sequence of thisdisclosure, according to an embodiment; and

FIG. 46 depicts comparative waveform diagrams of system efficiency for aconventional three-phase motor, and system efficiency a motor configuredand controlled according to the six-phase commutation sequence of thisdisclosure, according to an embodiment.

Corresponding reference numerals indicate corresponding parts throughoutthe several views of the drawings.

DETAILED DESCRIPTION

The following description illustrates the claimed invention by way ofexample and not by way of limitation. The description clearly enablesone skilled in the art to make and use the disclosure, describes severalembodiments, adaptations, variations, alternatives, and uses of thedisclosure, including what is presently believed to be the best mode ofcarrying out the claimed invention. Additionally, it is to be understoodthat the disclosure is not limited in its application to the details ofconstruction and the arrangements of components set forth in thefollowing description or illustrated in the drawings. The disclosure iscapable of other embodiments and of being practiced or being carried outin various ways. Also, it is to be understood that the phraseology andterminology used herein is for the purpose of description and should notbe regarded as limiting.

As shown in FIGS. 1-4, according to an embodiment of the invention, apower tool 10 is provided including a housing 12 having a gear case 14,a motor case 16, a handle portion 18, and a battery receiver 20. FIG. 1provides a perspective view of the tool 10. FIG. 2 provides a side viewof tool 10 including its internal components. FIGS. 3 and 4 depict twoexploded views of tool 10. Power tool 10 as shown herein is an anglegrinder with the gear case 14 housing a gear set (not shown) that drivesa spindle 24 arranged to be coupled to a grinding or cutting disc (notshown) via a flange (or threaded nut) 25 and guarded by a disc guard 26.It should be understood, however, that the teachings of this disclosuremay apply to any other power tool including, but not limited to, a saw,drill, sander, and the like.

In an embodiment, the motor case 16 attaches to a rear end of the gearcase 14 and houses a motor 28 operatively connected to the gear set 22.The handle portion 18 attaches to a rear end 30 of the motor case 16 andincludes a trigger assembly 32 operatively connected to a control module11 disposed within the handle portion 18 for controlling the operationof the motor 28. The battery receiver 20 extends from a rear end 31 ofthe handle portion 18 for detachable engagement with a battery pack (notshown) to provide power to the motor 28. The control module 11 iselectronically coupled to a power module 34 disposed substantiallyadjacent the motor 28. The control module 11 controls a switchingoperation of the power module 34 to regulate a supply of power from thebattery pack to the motor 28. The control module 11 uses the input fromthe trigger assembly 32 to control the switching operation of the powermodule 34. In an exemplary embodiment, the battery pack may be a 60 voltmax lithium-ion type battery pack, although battery packs with otherbattery chemistries, shapes, voltage levels, etc. may be used in otherembodiments.

In various embodiments, the battery receiver 20 and battery pack may bea sliding pack disclosed in U.S. Pat. No. 8,573,324, hereby incorporatedby reference. However, any suitable battery receiver and battery backconfiguration, such as a tower pack or a convertible 20V/60V batterypack as disclosed in U.S. Pat. No. 9,406,915, filed May 18, 2015, alsoincorporated by reference, can be used. The present embodiment isdisclosed as a cordless, battery-powered tool. However, in alternateembodiments power tool can be corded, AC-powered tools. For instance, inplace of the battery receiver and battery pack, the power tool 10include an AC power cord coupled to a transformer block to condition andtransform the AC power for use by the components of the power tools.Power tool 10 may for example include a rectifier circuit adapted togenerate a positive current waveform from the AC power line. An exampleof such a tool and circuit may be found in US Patent Publication No.2015/0111480, filed Oct. 18, 2013, which is incorporated herein byreference in its entirety.

Referring to FIG. 2, the trigger assembly 32 is a switch electricallyconnected to the control module 11 as discussed above. The triggerassembly 32 in this embodiment is an ON/OFF trigger switch pivotallyattached to the handle 18. The trigger 32 is biased away from the handle18 to an OFF position. The operator presses the trigger 32 towards thehandle to an ON position to initiate operation of the power tool 10. Invarious alternate embodiments, the trigger assembly 32 can be a variablespeed trigger switch allowing the operator to control the speed of themotor 28 at no-load, similar to variable-speed switch assembly disclosedin U.S. Pat. No. 8,573,324, hereby incorporated by reference. However,any suitable input means can be used including, but not limited to atouch sensor, a capacitive sensor, or a speed dial.

In an embodiment, power tool 10 described herein is high-power powertool configured to receive a 60V max battery pack or a 60V/20Vconvertible battery pack configured in its 60V high-voltage-rated state.The motor 28 is accordingly configured for a high-power application witha stator stack length of approximately 30 mm. Additionally, as laterdescribed in detail, the power module 34, including its associated heatsink, is located within the motor case 16 in the vicinity of the motor28. Additionally and/or alternatively, power tool 10 may be have alow-voltage rating (e.g., 20V) or mid-voltage rating (e.g., 40V) adaptedto receive a 20V max or a 40V max battery pack.

While embodiments depicted herein relate to a DC-powered power toolpowered by a battery pack, it is noted that the teachings of thisdisclosure also apply to an AC-powered tool, as disclosed in US PatentPublication No. 2015/0111480, which is incorporated herein by referencein its entirety. In this embodiment, a power cord may be providedinstead of battery receiver 20. The power tool 10 may be configured toreceive AC supply having a nominal voltage of, for example, 120VAC.Alternatively, power tool 10 may be configured to receive AC supplyhaving a nominal voltage of, for example, 230VAC.

Additionally and/or alternatively, the teachings of this disclosure alsoapply to an AC/DC power tool, as disclosed in WO2015/179318 filed May18, 2015, which is incorporated herein by reference in its entirety. Inthis case, the power tool may be provided with a battery receptacle 20as well as a power cord (not shown). Alternatively, an AC/DC poweradaptor may be provided to supply one of AC or DC power to the powertool via the battery receiver 20, as described in detail in the '318application.

FIGS. 5A and 5B depict two perspective views of motor 28, according toan embodiment. FIG. 6 depicts an exploded view of the motor 28,according to an embodiment. As shown in these figures, the motor 28 is athree-phase brushless DC (BLDC) motor having a can or motor housing 29sized to receive a stator assembly 70 and a rotor assembly 72. Variousaspects and features of the motor 28 are described herein in detail. Itis noted that while motor 28 is illustratively shown in FIGS. 1-4 as apart of an angle grinder, motor 28 may be alternatively used in anypower tool or any other device or apparatus.

In an embodiment, rotor assembly 72 includes a rotor shaft 74, a rotorlamination stack 76 mounted on and rotatably attached to the rotor shaft74, a rear bearing 78 arranged to axially secure the rotor shaft 74 tothe motor housing 29, a sense magnet ring 90 attached to a distal end ofthe rotor shaft 74, and fan 37 also mounted on and rotatably attached tothe rotor shaft 74. In various implementations, the rotor laminationstack 76 can include a series of flat laminations attached together via,for example, an interlock mechanical, an adhesive, an overmold, etc.,that house or hold two or more permanent magnets (PMs) therein. Thepermanent magnets may be surface mounted on the outer surface of thelamination stack 76 or housed therein. The permanent magnets may be, forexample, a set of four PMs that magnetically engage with the statorassembly 70 during operation. Adjacent PMs have opposite polarities suchthat the four PMs have, for example, an N—S—N—S polar arrangement. Therotor shaft 74 is securely fixed inside the rotor lamination stack 76.Rear bearing 78 provide longitudinal support for the rotor 74 in abearing pocket (described later) of the motor housing 29.

In an embodiment, stator assembly 70 includes a generally cylindricallamination stack 80 having center bore configured to receive the rotorassembly 72. Lamination stack 80 further includes a plurality of statorteeth extending inwardly from a stator ring towards the center bore. Thestator teeth define a plurality of slots there between configured. Aplurality of coil windings 86 are wound around the stator teeth 82 intothe slots. Coil windings 86 may be wound and connected together invarious configurations, as discussed later in detail. In an embodiment,where motor 28 is a three-phase BLDC motor, a total of six coil windings86 may be provided. Terminals 104 are coupled to the coil windings 86.Although three terminals 104 are depicted herein, in an embodiment, oneterminal 104 may be provided for each coil winding 86 for a total of sixterminals 104.

In an embodiment, fan 37 of the rotor assembly 72 includes a back plate60 having a first side 62 facing the motor case 16 and a second side 64facing the gear case 14. A plurality of blades 66 extend axiallyoutwardly from first side 62 of the back plate 60. Blades 64 rotate withthe rotor shaft 44 to generate an air flow as previously discussed. Whenmotor 28 is fully assembled, fan 37 is located at or outside an open endof the motor housing 28 with a baffle 330 arranged between the statorassembly 70 and the fan 37. The baffle 33 guides the flow of air fromthe blades 64 towards the exhaust vents 58.

Power module 34 in the illustrated example is provided adjacent themotor housing 29. In an embodiment, power module 34 includes a heat sinkand a circuit board. Power switching components, as will be describedlater in detail, may be mounted on the circuit board in close proximityto the heat sink. In an embodiment, a series of positional sensors(e.g., hall sensors) may also be provided as a part of the power module34 close proximity to sense magnet ring 90 to sense the magneticrotational position of the sense magnet ring 90. In this embodiment,terminals 104 protrude from the back of the motor housing 29 and arereceived into corresponding slots of the power module 34.

It must be understood that while power module 34 in this embodiment isprovided adjacent the motor housing 29, the circuit board for the powerswitching components may be provided anywhere in the power tool,including, but not limited to, below the motor housing 29, or in thehandle portion 18. In other power tools, such as drills or impactdrivers, the circuit board may be provided in the tool handle. Anexample of such an arrangement is disclosed in US Patent Publication No.2015/0280517, which is incorporated herein by reference in its entirety.

FIG. 7 depicts an exemplary block circuit diagram for controlling thecommutation of BLDC motor 202 for an AC/DC power tool 200. As shown inthis figure, power tool 200 may include a motor control circuit 204disposed between a power supply interface 216 and motor 202 to controlsupply of power from the power supply interface 216 to motor 202.

In an embodiment, power supply interface 216 is configured to receivepower from one or more of the aforementioned DC power supplies and/or ACpower supplies. The power supply interface 216 is electrically coupledto the motor control circuit 204 by DC power lines DC+ and DC− (fordelivering power from a DC power supply) and by AC power lines ACH andACL (for delivering power from an AC power supply). In an embodiment, inorder to minimize leakage and to isolate the DC power lines DC+/DC− fromthe AC power lines ACH/ACL, a power supply switching unit 215 may beprovided between the power supply interface 216 and the motor controlcircuit 204. The power supply switching unit 215 may be utilized toselectively couple the motor 202 to only one of AC or DC power supplies.Switching unit 215 may be configured to include relays, single-poledouble-throw switches, double-pole double-throw switches, or acombination thereof. In the illustrative example, switching unit 215includes two power supply switching units 216 and 218, in this case twodouble-pole double-throw switches, which receive the DC power linesDC+/DC− and the AC power lines ACH/ACL, and output the same signals tothe motor control circuit 204.

In an embodiment, motor control circuit 204 includes a power unit 206and a control unit 208.

In an embodiment, power unit 206 includes a power switch circuit 226that is coupled to motor 202 terminal to drive the motor windings. Aspreviously discussed, the power switch circuit 226 may include sixsemi-conductor switching components configured as a three-phaserectifier bridge circuit and disposed in power module 34.

In an embodiment, power unit 206 is additionally provided with a with arectifier circuit 220. In an embodiment, power from the AC power linesACH and ACL is passed through the rectifier circuit 220 to convert orremove the negative half-cycles of the AC power for compatibility withmotor 202. In an embodiment, rectifier circuit 220 may include afull-wave bridge diode rectifier 222 to convert the negative half-cyclesof the AC power to positive half-cycles and output a DC bus line 221.Alternatively, in an embodiment, rectifier circuit 220 may include ahalf-wave rectifier to eliminate the half-cycles of the AC power. The DCbus line is coupled to the input terminals of the power switch circuit226. In an embodiment, rectifier circuit 220 may further include a buscapacitor 224 provided across the DC bus line 221. In an embodiment,capacitor 224 may have a relatively small value of, for example, 5 to 50uF, designed to remove part of the high frequency noise from the busvoltage. The DC power lines DC+ and DC− bypass the rectifier circuit 220and is coupled directly to the DC bus line 221.

In an embodiment, control unit 208 includes a controller 230, a gatedriver 232, a power supply regulator 234, and a power switch 236. In anembodiment, controller 230 is a programmable device arranged to controla switching operation of the power devices in power switching circuit226. In an embodiment, controller 230 receives rotor rotational positionsignals from a set of position sensors 238 provided in close proximityto the motor 202 rotor. In an embodiment, position sensors 238 may beHall sensors. It should be noted, however, that other types ofpositional sensors may be alternatively utilized. It should also benoted that controller 230 may be configured to calculate or detectrotational positional information relating to the motor 202 rotorwithout any positional sensors (in what is known in the art assensorless brushless motor control). Controller 230 also receives avariable-speed signal from variable-speed actuator (not shown) discussedabove. Based on the rotor rotational position signals from the positionsensors 238 and the variable-speed signal from the variable-speedactuator, controller 230 outputs drive signals UH, VH, WH, UL, VL, andWL through the gate driver 232, which provides a voltage level needed todrive the gates of the semiconductor switches within the power switchcircuit 226 in order to control a PWM switching operation of the powerswitch circuit 226.

In an embodiment, power supply regulator 234 may include one or morevoltage regulators to step down the power supply from power supplyinterface 128-5 to a voltage level compatible for operating thecontroller 230 and/or the gate driver 232. In an embodiment, powersupply regulator 234 may include a buck converter and/or a linearregulator to reduce the power voltage of power supply interface 128-5down to, for example, 15V for powering the gate driver 232, and down to,for example, 3.2V for powering the controller 230.

In an embodiment, power switch 236 may be provided between the powersupply regulator 234 and the gate driver 232. Power switch 236 may be anON/OFF switch coupled to the ON/OFF trigger or the variable-speedactuator to allow the user to begin operating the motor 202, asdiscussed above. Power switch 236 in this embodiment disables supply ofpower to the motor 202 by cutting power to the gate drivers 232. It isnoted, however, that power switch 236 may be provided at a differentlocation, for example, within the power unit 206 between the rectifiercircuit 220 and the power switch circuit 226. It is further noted thatin an embodiment, power tool 128 may be provided without an ON/OFFswitch 236, and the controller 230 may be configured to activate thepower devices in power switch circuit 226 when the ON/OFF trigger (orvariable-speed actuator) is actuated by the user.

While the circuit diagram above is provided for an AC/DC system, it mustbe understood that a similar circuit may be employed for an AC-only or aDC-only system with a modified power supply interface 216 and withoutthe switching unit 215. It must also be understood that an AC/DC systemmay include a circuit wherein a single power interface is configured toreceive only one of an AC power supply or a DC power supply at a giventime, thus without the need for a switching unit 215 as shown.

Dual-Inverter for BLDC Motors and Multi-Voltage Power Supplies

One aspect of the invention is described herein with reference to FIGS.8-15, according to an embodiment of the invention.

Two types of commonly used semiconductor power switches for driving aBLDC motor are FETs (Field-Effect Transistors) and IGBTs (Insulated-GateBipolar Transistors). While both provide benefits of a solid-statesolution for motor control applications, they exhibit differentcharacteristics and are suitable for different voltage and powerapplications. While FETs support high frequency switching applicationsand reduce switching losses, IGBTs have better durability to highcurrent. Thus, IGBTs are often associated with higher voltageapplications, and FETs are used in relatively low voltage and low powerapplications. Accordingly, in an embodiment, in power tool designed tooperate at a low or mid rated voltage range (e.g., less than 100V), thepower switching components in the three-phase inverter bridge are FETs.Also, in power tool designed to operate at a high-rated voltage range(e.g., 100V or above), the power switching components in the three-phaseinverter bridge are IGBTs.

U.S. patent application Ser. No. 14/715,258 filed May 18, 2015, which isincorporated herein by reference in its entirety, describes variousAC/DC power tool configurations using power supplies having comparableor disparate power supply voltage ratings. For example, in anembodiment, an AC/DC power tool may include two battery receptaclesdesigned to receive two 60V battery packs for a total of 120V DC power,and an AC power cord adapted to receive 120V AC power. Alternatively, anAC/DC power tool may operate with power supplies having disparatevoltage ratings, i.e., where voltage provided by the AC power supply hasa nominal voltage that is significantly different from a nominal voltageprovided from the DC power supply. For example, the tool may include twobattery receptacles designed to receive two 60V battery packs for atotal of 120V DC power, and an AC power cord adapted to receive 230V ACpower (e.g., in Europe). Yet alternatively, an AC/DC power tool mayinclude a single battery receptacle designed to receive a nominalvoltage of 40V-80V (e.g., from a single battery pack), and an AC powercord adapted to receive a nominal voltage of 100V-120V AC power. Inthese configurations, the power switching components may be suitable forone power supply voltage rating but not another.

It is initially noted that while the embodiments of this disclosure aredescribed herein with reference to an AC/DC system, principles of thisdisclosure may apply to any multi-voltage system, including, but notlimited to, DC-only power tools configured to operate with various DCpower supplies (e.g., a single 60V battery pack or two 60V battery packconnected in series).

Referring now to FIG. 8, an improved exemplary block circuit diagram forcontrolling the commutation of BLDC motor 302 for an AC/DC power tool300 is depicted, according to an embodiment. In this embodiment, powertool 300 may include a motor control circuit 304 including a power unit306 and a control unit 308. Similarly to FIG. 7, control unit 308includes a controller 330, a gate driver 332, a power supply regulator334, and a power switch 336. Power unit 306 is disposed between powersupply interface (not shown for the sake of simplicity) and the motor302. Power supply interface receives electric power from a DC powersupply 310 and/or an AC power supply 312. The power line from the ACpower supply is coupled to a bridge rectifier 322 and a bus capacitor324 to produce a positive waveform. Unlike the embodiment of FIG. 7,power unit 306 includes two power switching circuits: a FET switchcircuit 326 disposed on a first DC bus line 325 between the DC powersupply 310 and the motor 302, and an IGBT switch circuit 328 disposed ona second DC bus line 327 between the AC power supply 312 and the motor302. Using this arrangement, FETs are utilized for motor commutation inlow-voltage DC-powered applications and IGBTs are utilized for motorcommutation in higher-voltage/higher power AC applications.

FIG. 9 depicts an exemplary FET switch circuit 326, according to anembodiment. FIG. 10 depicts an exemplary IGBT switch circuit 328,according to an embodiment. In each of these embodiments, a three-phaseinverter bridge circuit is provided including three high-side powerswitches and three low-side power switches. The gates (or bases) of thehigh-side and low-side power switches are driven by controller 330 viathe gate drivers 332. In an embodiment, the sources (or emitters) of thehigh-side power switches are coupled to the drains (or collectors) ofthe low-side power switches to output power signals PU, PV, and PW fordriving the BLDC motor 202.

In an embodiment, the controller 330 determines the power mode andactivates one of the FET switch circuit 326 and/or the IGBT switchcircuit 328 accordingly. The controller 330 may do so by sensing voltageon one of the bus lines 325 or 327. Alternatively, the power supplyinterface (not shown) or the power supply regulator 334 may determinewhich of the bud lines 325 or 327 carries electrical power and send asignal indicative of the power mode to the controller 330.

In one embodiment of the invention, the motor windings are wound inpairs such that a single phase is wound around two oppositely-arrangedteeth of the motor. The three phases are connected in a wye or deltaconfiguration and electrically connected to the PV, PW, and PU outputsof both the FET switch circuit 326 and the IGBT switch circuit 328.While this arrangement can be made without considerable changes to themotor 302, usage of the same coil windings in high-voltage andlow-voltage may lead to low efficiency.

In an alternative embodiment, the as shown in FIGS. 11A and 11B, the sixmotor teeth are wound separately to form six electrically-isolatedwindings. The first set of windings A-C are connected to the outputs ofthe FET switch circuit 326, and the second set of windings D-F areconnected to the outputs of the IGBT switch circuit 328. The first setof windings in this embodiment is optimized for application of lowvoltage and high current, whereas the second set of windings isoptimized for application of high voltage and low current. Generally,the number of turns on each coil of the motor is directly proportionalto the induced back electro-magnetic force (back-EMF) in the motorwindings. Thus, for a motor optimized to operate with a low voltagepower supply, the motor is generally configured with a lower number ofturns per winding in comparison to a motor optimized to operate with ahigh voltage power supply, provided that both motors have the sameoutput speed and power output requirements. In other words, given thesame speed and power output performance, low voltage/high currentapplications typically require a smaller number of turns of motorwindings, and low current/high voltage applications require thinnerwires with a larger number of turns. Given the same slot area, highernumber of turns requires use of thinner magnet wires. Accordingly, in anembodiment, the first set of windings A-C may be provided with thickermagnet wires and a low number of turns for low voltage/high currentapplications, and the second set of windings D-F may be provided withthinner magnet wires and a higher number of turns for high voltage/lowcurrent applications.

In the above-described embodiment, winding the coils on a single statortooth instead of a pair of teeth effectively adversely decreases themagnetic field provided in each phase, thus reducing the speed and/orpower output of the motor. This difference may be compensated, accordingto an embodiment, by increasing the length of the lamination stack.

FIG. 12 depicts a speed-torque diagram showing a comparison of threeexemplary motors, according to an embodiment. FIG. 13 depicts apower-torque diagram shown a comparison of the same exemplary motors,according to an embodiment. The first motor (corresponding to theprofile represented in solid lines) includes a stator stack of 25laminations and is fully wound using the conventional method of windingtwo teeth for each phase. The second motor (corresponding to the profilerepresented in dotted lines) includes a stator stack of the same lengthbut wound using a single tooth per phase. In other words, only three ofthe six stator teeth are wound in this motor. As shown in these figures,using a single tooth winding per phase in the second motor decreases thespeed and power performance of the motor, particularly with increasedtorque. The third motor (corresponding to the profile represented indashed lines) includes a stator stack of 30 laminations wound using asingle tooth per phase. As shown in these figures, the third motor hascomparable speed and power output performance to the first motor. It isnoted that all three motors are wound using wires of the same thicknessand with the same number of turns. Accordingly, while using a singletooth per phase decreases motor power and speed performance, increasingthe stack length by approximately 10% to 30%, preferably byapproximately 20% (i.e., from 25 to 30 laminations) compensates for thatdecrease and provides comparable motor speed and power output.

According to an embodiment of the invention, FET switch circuit 326 andIGBT switch circuit 328 may be controlled in a hybrid mode where both DCand AC power supplies 310 and 312 are used in tandem. This may occur inhigh power applications where neither power source can sufficientlyhandle the high current draw. In an embodiment, the power tool 300 iscoupled to both the DC and AC power supplies 310 and 312 and thecontroller 330 executes a proper commutation algorithm on both the FETswitch circuit 326 and IGBT switch circuit 328 concurrently. Accordingto this embodiment, power output in exceed of 1800 watts can be achievedwithout tripping a standard 15 amp circuit breaker.

FIG. 14 depicts an exemplary current diagram of the DC and AC linecurrents being supplied through the power supplies 310 and 312 in thehybrid mode, according to an embodiment. In this embodiment, the ACpower supply 312 has a 120VAC RMS voltage and the DC power supply 310 isa lithium ion battery pack having a maximum voltage of 60VDC. As shownherein, the AC current peaks at about 35 amps within each AC cycle, foran average RMS current of approximately 14 amps. The AC power supply 312has an average current of approximately 18 amps. This allows the tool todraw substantially more current to reach a desired power output levelnormally not achievable from a single power source alone.

In an embodiment, the controller 330 may be configured to employ varioustechniques to optimize current draw from the DC power supply 310 asneeded. For example, the controller 330 may enable current draw from theDC power supply 310 only when the current drawn by the motor 302 exceedsa predetermined threshold of, e.g., 14 amps. Alternatively and/oradditionally, the controller 330 may enable draw current from the DCpower supply 310 for several degrees before and after the zero crossingsof the AC power supply 312 voltage, where current drawn from the ACpower supply 312 is at a minimum, to supplement the AC power supply 312.U.S. patent application Ser. No. 14/876,458 filed Oct. 6, 2015, which isincorporated by reference in its entirety, includes some examples ofhybrid power control schemes that can be utilized in the presentembodiment.

Referring now to FIG. 15, an additional and/or improved embodiment ofthe invention is depicted, according to an embodiment. This figure issimilar to FIG. 8 and includes a circuit 300 having two power switchinginverter circuits 326 and 328. Additionally, in this figure, circuit 300is provided with a charging circuit 350 enabling the tool to charge thebattery 310 when the tool is coupled to an AC power source 312. In anembodiment, the charging circuit 350 may be receive power from the ACbus line 327 or the motor terminals (in this case terminals D and F).The details of the charging circuit 350 is beyond the scope of thisdisclosure, but in short, the charging circuit 350 may include a powerregulator (not shown) that provides a suitable voltage level (e.g., 20Vor 60V, depending on the battery configuration) for charging the battery310. The charging circuit 350 may also include a switch (not shown)controllable by the controller 330. The circuit 330 may also be providewith additional wiring and circuitry to provide the controller 330 withvoltage sense signals from the battery 310. This allows the controllerto monitor the voltage of the battery cells and regulate the supply ofcharging power to the battery 310 via the aforementioned switchaccordingly.

Dual-Inverter for Dual-Battery Applications

A hybrid design including an AC power supply and a DC power supply wasdescribed above with reference to FIG. 14. Another aspect of theinvention described herein with reference to FIGS. 16-22 fordual-inverter for a power system being powered by two or more DC powersupplies.

Power tool applications powered by multiple DC power supplies, forexample, power tools including two or more battery receptacles, areknown. In such applications, the battery receptacles places thebatteries in series to increase the total voltage supplied to the motor.For example, the two battery receptacles may receive two 60V max batterypacks. The battery receptacles are connected in such a way that thebattery packs are placed in series to supply a total maximum voltage of120V to the motor.

While a series power supply configuration described above is suitablefor high voltage applications, a power supply parallel configuration maybe suitable in some power tool applications, for example, for a powertool having an operating voltage of around 60V and designed to receive60V max battery packs, or a power tool having an operating voltage ofaround 20V and designed to receive 20V max battery packs. In suchapplications, if power tool ergonomics allow inclusion of two batteryreceptacles, connecting the battery packs in parallel may provide manyadvantages. Namely, using the parallel configuration, the user canoperate the tool and obtain similar speed performance using one or bothbatteries, though using both batteries will increase runtime. Also,since the operating voltage of the power tool remains the same as thebattery packs, there is no need to modify the power tool housing toprovide double-insulation for the motor.

One way to achieve a parallel connection between battery packs is byconnecting the terminals of the battery packs in parallel, e.g., bycommonly coupling the terminals to the same DC bus line. Thisarrangement may work if the two battery packs have the same state ofcharge. However, if one of the batteries has a lower state of charge,current through the higher-voltage battery pack flows into thelower-voltage battery pack at least during a part of each commutationcycle. FIG. 16 depicts an exemplary circuit diagram for two 20V maxbattery packs coupled in parallel at the battery receptacle terminals,one (battery A) fully charged at 20V, and the second (battery B) chargedto 18V. In this figure, significant current draw is being made frombattery A, while current draw from battery B is minimal and at timesnegative.

Referring now to FIG. 17, an exemplary block circuit diagram forcontrolling the commutation of BLDC motor 362 for a DC-only power tool360 powered by two DC power supplies 370 and 372 is depicted, accordingto an embodiment. In this embodiment, power tool 360 may include a motorcontrol circuit 364 having a power unit 366 and a control unit 368.Similarly to FIG. 7 previously discussed, control unit 368 may include acontroller 390, a gate driver 392, a power supply regulator 394, and apower switch 396. The controller 390 receives motor 362 positionalsignals from position sensors 398. Power unit 366 is disposed betweenthe motor 362 and the two DC power supplies 370 and 372. In anembodiment, the power supplies 370 and 372 are battery packs received intwo battery receptacles of the power tool 360, though it must beunderstood that any DC power supply, e.g., from a generator or anadaptor, may be used as a power supply. It must also be understood thatthe principles described herein may be applied to a power tool with morethan two DC power supplies.

In an embodiment, power unit 366 includes a first switch circuit 386coupled to the first DC power supply 370 via a first DC bus line 385,and a second switch circuit 388 coupled to the second DC power supply372 via a second DC bus line 387. The outputs of the first switchcircuit 386 are coupled to windings A-C of the motor 362. The outputs ofthe second switch circuit 388 are coupled to windings D-F of the motor362. These windings are configured as shown in FIGS. 11A and 11Bpreviously discussed.

In an embodiment, power unit 366 further includes a battery selectorswitch 352 disposed in this example on the second DC bus line 387arranged to coupled one of the first DC power supply 370 or second DCpower supply 372 to the second switch circuit 388. In an embodiment,battery selector switch 352 is switchable via a user-actuated switch ora mechanical switch coupled to the power tool 360 battery receptacles.In this embodiment, battery selector switch 352 couples the first DCpower supply 370 to the second switch circuit 388 when no second DCpower supply 372 is provided, and couples the second DC power supply 373to the second switch circuit 388 when one is provided. As such, when thepower tool is operated using a single power supply 370, the power supply370 is coupled to all the motor windings.

In an embodiment, controller 390 controls motor 362 commutation byconcurrently driving the first and second switch circuits 386 and 388.In an embodiment, the controller 390 outputs one set of drive signals(i.e., UH-WH and UL-WL as shown in FIGS. 9 and 10) coupled to both thefirst and second switch circuits 386 and 388.

In an embodiment, where the tool 360 is designed to receive low voltagebattery packs (e.g., 10-40VDC), each of the first and second switchcircuits 386 and 388 may be configured using FETs, as shown in FIG. 9.In an embodiment, where the tool 360 is configured to receive at leastone relatively higher-voltage battery pack, one or both of the first andsecond switch circuits 386 and 388 may be configured using IGBTs, asshown in FIG. 10.

The above-described embodiment effectively provided a parallelconnection between two DC power supplies 370 and 372 (e.g., two batterypacks) while isolating the current paths of the two battery packs. Thus,if one of the battery packs has a lower state of charge, it does notdraw current from the higher-voltage battery pack as in the example ofFIG. 16.

FIG. 18 depicts an exemplary current diagram for two 20V max batterypacks coupled in parallel via the dual-inverter configuration describedhere, one (battery A) fully charged at 20V, and the second (battery B)charged to 18V. In this figure, while the current draw from battery A ishigher than the current draw from battery B, it is lower in comparisonthe current draw in FIG. 16. Furthermore, positive current draw is beingmade from battery B.

This arrangement allows the user to operate the power tool using asingle battery pack, which provides comparable power output and speedperformance as a conventional three-phase motor and drive circuit, orusing two battery packs, which provides improved power output and speedperformance at approximately twice the battery life.

Specifically, as shown in the current (battery)/torque diagram of FIG.19, when using two battery packs in the parallel connection describedherein, the current draw from each battery pack is halved as expected.This approximately doubles the power tool runtime when using bothbattery packs. In addition, since current draw from each battery islower, the voltage drop of each battery due to battery impedance is alsoproportionally lowered. This decreased battery impedance significantlyenhances the power output capability of the two battery packs combined,as shown in the power/torque diagram of FIG. 20. Maximum speed andsystem efficiency are similarly improved, as shown in the speed/torquediagram of FIG. 21 and the efficiency/torque diagram of FIG. 22.

In an embodiment, the amount of current and consequently the amount ofpower from each DC power supply 370 and 372 (e.g., two battery packs)may be independently controlled by selecting the appropriate conductionangle and/or advance angle. As described in WO2015/179318 filed May 18,2015, which is incorporated by reference in its entirety, the conductionband (i.e., conduction angle) of each phase of the motor may be variedfrom the default 120 degrees to a lesser value (e.g., 90 degrees) fordecreased power output, or to a higher value (e.g., 150 degrees) forincreased power output. Similarly, the advance angle may be varied fromthe default 30 degrees to a lesser value (e.g., 20 degrees) fordecreased power output, or to a higher value (e.g., 50 degrees) forincreased power output. In an embodiment, at least one of the conductionband or angle advance may be set in accordance with a condition relatedto the DC power supply 370 and 372. In an embodiment, the condition maybe the state of the charge of the battery packs. Thus, for example, afully charged battery pack may be fired with a condition band/angleadvance (CB/AA) of 120/30 degrees, whereas a partially charged batterypack may be fired with a CB/AA of 150/45 degrees.

Dual-Inverter for Series/Parallel Winding Configuration

Another aspect of the invention is described herein with reference toFIG. 23-32.

In a three-phase BLDC motors, the stator windings may be wound in avariety of configurations. The two basic winding configurations for thephases of the motor are wye and delta connections. A motor with windingsconfigured in the delta configuration can operate at a greater speedthan the same windings configured in the wye configuration. However, amotor with windings configured in the wye configuration can operate witha greater torque than the same windings configured in the deltaconfiguration.

Furthermore, the motor windings for each phase of the motor may also beconfigured in series or parallel connections. In a series windingconnection, where the two coils of the same phase are stacked in series,the number of turns of the coils add up. Thus, a motor with windingsconfigured in a series connection is suitable for high voltage/lowtorque applications, where a higher total number of winding turns isneeded. In a parallel winding connection, where the two coils of thesame phase are wired in parallel to each other, the total number ofturns for each phase do not add up, but the back-EMF of the motor isdecreased by half in comparison to the series connection (and resistanceis decreased by a fourth). Accordingly, a motor with windings configuredin a parallel configuration is suitable for low voltage/high currentapplications, where a higher number of winding turns is not required,but a reduced back-EMF voltage is desired. Specifically, given the samemotor and the same power and speed output requirements, a seriesconnection is more suitable for high voltage applications, e.g. powertools operating with a power supply having a rated voltage ofapproximately 200-240V, and a parallel connection is more suitable forrelatively lower voltage applications, e.g. power tools operating with apower supply having a rated voltage of approximately 100-120V. It isnoted that these voltage ranges are exemplary and these principles applyto other comparative voltage ranges, e.g., a series connection for100-120V voltage range and a parallel connection for a 50-60V voltagerange.

FIGS. 23 and 24 respectively depict exemplary winding configurations fora wye-series connection and a wye-parallel connection for illustrationpurposes, according to an embodiment.

Traditionally the series or parallel connections are facilitated on themotor itself, e.g., via wire connections on the motor stator. Thiscomplicates the motor manufacturing process where, for example, a cordedpower tool being manufactured for sale in the US and Europe.

According to an embodiment, the motor winding series or parallelconnection is facilitated via a two inverter design, as describedherein.

Referring to FIG. 25, an exemplary block circuit diagram for controllingthe commutation of BLDC motor 402 for an AC power tool 400 is depicted,according to an embodiment. In this embodiment, power tool 400 mayinclude a motor control circuit 404 having a power unit 406 and acontrol unit 408. Similarly to FIG. 7 previously discussed, control unit408 includes a controller 430, a gate driver 432, a power supplyregulator 434, and a power switch 436. Power unit 406 is disposedbetween AC power supply 412 and the motor 402. Power unit 406 includesbridge rectifier 422 and a bus capacitor 424 to produce a positivewaveform on the DC bus line 425.

It is initially noted that while this embodiment is described hereinwith reference to an AC-only power tool system, the principles disclosedherein may similarly apply to a DC-only or an AC/DC power tool system.

In this embodiment, power unit 406 includes two power switchingcircuits: a first switch circuit 426 and a second switch circuit 428.Each of the first and second switching circuits 426 and 428 may includeFETs or IGBTs depending on the voltage rating of the power supply 412.The power terminals of both the first and second switching circuits 426and 428 are coupled to the DC bus line 425. The outputs of the firstswitch circuit 426 are coupled to windings A-C of the motor 402. Theoutputs of the second switch circuit 428 are coupled to windings D-F ofthe motor 402. These windings are configured as shown in FIGS. 11A and11B previously discussed. By driving the two switch circuits 426 and 428concurrently (i.e., using the same commutation drive signals), thisconfiguration allows windings A and D of the motor to be connected anddriven in parallel. Similarly, windings B and F, and windings C and Fare connected and driven in parallel. Thus, this configuration employs aparallel winding connection on the motor without hardwiring the motorstator windings in a parallel configuration.

FIG. 26 depicts a similar exemplary block diagram as FIG. 25 describedabove, but with the first and second switch circuits 426 and 428connected so as to facilitate a series winding connection on the motor402. In this embodiment, the DC bus line 425 is connected to thepositive terminal (+) of the first switching circuit 426 and thenegative terminal (−) of the second switch circuit 428. The positiveterminal (+) of the second switching circuit 428 is coupled to thenegative terminal (−) of the first switch circuit 426. The outputs ofthe first switch circuit 426 are coupled to windings A-C of the motor402, and the outputs of the second switch circuit 428 are coupled towindings D-F of the motor 402. These windings are configured as shown inFIGS. 11A and 11B previously discussed.

By driving the two switch circuits 426 and 428 concurrently (i.e., usingthe same commutation drive signals), this configuration allows windingsA and D of the motor to be connected and driven in series. Specifically,for each cycle of the rectified AC waveform on the DC bus line 425, acurrent path is provided through the positive terminal (+) of the firstswitch circuit 426, into motor winding A, and through the negativeterminal (−) of the first switch circuit 426 and the positive terminal(+) of the second switch circuit 428, into motor winding D. Similarly,windings B and F, and windings C and F are connected and driven inseries. Thus, this configuration employs a series winding connection onthe motor without hardwiring the motor stator windings in a parallelconfiguration.

Another advantage of the dual-inverter design for a series windingconnection is the ability to use smaller and less expensive powerswitches for high power application, as described herein.

FIG. 27 depicts a voltage waveform diagram for a conventionalthree-phase BLDC motor wound in a series connection and driven via asingle three-phase inverter circuit. In this diagram, line 450represents the AC power supply voltage (e.g., 120VAC rms mains) and line452 represents the voltage across the inverter switches. In this design,the inverter switches have to be rated to handle a voltage of 120V.Where the AC mains is 240VAC, the inverter switches have to be similarlyrated to handle a voltage of 240V, and thus are substantially larger andmore expensive.

FIG. 28 depicts a voltage waveform diagram corresponding to the circuitdiagram of FIG. 25, according to an embodiment. In this diagram, line450 represents the AC power supply voltage 412 (e.g., 120VAC rms mains,also referred to as the nominal voltage of the AC power supply voltage412) and line 454 represents the voltage across the inverter switches inthe first switch circuit 426 and second switch circuit 428. Since thecorresponding inverter switches are connected in series, they equallyshare the voltage of the DC bus line 425. Thus, in this design, theinverter switches have to be rated to handle a voltage of half the ACpower supply, i.e., 60V. Where the AC mains is 240VAC, the inverterswitches have to be rated to handle a voltage of 1200V, which aresubstantially cheaper and smaller in comparison to 240V switches.

Accordingly, in the embodiment described above, the increase in thetotal inverter switches required to facilitate a series connection issignificantly offset by the use of smaller and less expensive inverterswitches.

Referring to FIG. 29, an exemplary block circuit diagram for controllingthe commutation of BLDC motor 402 for an AC power tool 400 is depicted,according to an alternative and/or additional embodiment of theinvention. In contrast to the embodiments of FIGS. 25 and 26, in thisembodiment, the first and second switch circuits 426 and 428 are nothardwired into a series or parallel connection. Rather, in thisembodiment, a switching unit 460 is further provided on the DC bus line425 to selectively couple the first and second switch circuits 426 and428 in a series or parallel connection. In an embodiment, the switchingunit 460 may include one or more switches that selectively couple thepositive and negative nodes of the DC bus line 525, the negative (−)terminal of the first switch circuit 426, and the positive (+) node ofthe second switch circuit 428 in such a way to selectively place theswitch circuits in either a series or a parallel connection.

FIG. 30 depicts an exemplary switch unit 460, according to anembodiment. In this embodiment, switch unit 460 includes two single-poledouble-throw switches 462 and 464. In their normally-closed position, inan embodiment, these switches 462 and 464 connect the DC Bus positive(+) and negative (−) terminals to the positive terminal of the secondswitch circuit 428 and the negative terminal of the first switch circuit426 to place the switch circuits in a parallel connection. When opened,e.g., via a mechanical actuator or other means, in an embodiment, theseswitches 462 and 464 disconnect the DC Bus positive (+) and negative (−)terminals from the positive terminal of the second switch circuit 428and the negative terminal of the first switch circuit 426, and insteadconnect latter terminals together to place the switch circuits in aseries connection.

FIG. 31 depicts a power output/torque waveform diagram for thedual-inverter design of this disclosure described above in the seriesconnection (coupled to a 230VAC 60 hz power supply) and in the parallelconnection (coupled to a 120VAC 50 hz power supply). FIG. 32 depicts anAC current/torque waveform diagram of the same. These measurementscorrespond to motor commutation at a conduction angle of 120 degreeswith an advance angle of 30 degrees. As shown herein, the twoconfigurations result in similar power output performance, withapproximately half the AC current for the 230V power supply.

Dual-Inverter for Improved Harmonics and Power Factor

Another aspect of the invention is described herein with reference toFIGS. 33-45, according to an embodiment.

Referring initially to FIG. 33, a current diagram for a conventionalthree-phase BLDC motor coupled to an AC power supply, is depicted. Thiscurrent diagram corresponds to the block diagram of FIG. 7 in the ACmode, in an exemplary embodiment. As shown, the motor phase current,represented by a dotted line and measured at the A terminal of themotor, has a substantially sinusoidal waveform. It is noted that in thisexample, the motor is connected in a wye configuration, and thereforethe motor line and phase currents are the same. By contrast, the ACinput line current, represented by a solid line, includes large spikesthat fluctuating between 0 to over 40 amps each time a phase of themotor is commutated, causes high frequency current harmonics. Thesecurrent spikes, which are attributable to the switching operation of thepower switch circuit 226 between the phases of the motor, significantlydecrease the tool's power factor.

As previously described, a motor stator may be wound in a delta or a wyeconfiguration. FIGS. 34 and 35 respectively depict a wye and a deltamotor configuration. Conventionally, in a six-slot four-pole motor, themotor windings are wounds on opposite teeth of the stator for each phaseand connected to one another in either a delta or a wye connection.

It is understood by those of ordinary skill in the art that a deltamotor connection exhibits a current phase shift compared to a wyeconnection in the respective phase winding. This phase shift isattributable to the current having two current paths through thewindings in the delta connection. Specifically, in a wye connection, themotor phase current is in line with the AC input line current, whereinas a delta connection, the motor phase current lags the AC input linecurrent by approximately 30 degrees. It was found by the inventors thatusing a two-invertor arrangement, as described herein, the motorwindings may be wound using a combination of wye and delta connectionsso as to utilize this current phase shift to improve current harmonicsand power factor, as described herein according to an embodiment of theinvention.

Referring to FIG. 36, an exemplary block circuit diagram for controllingthe commutation of BLDC motor 502 for an AC power tool 500 is depicted,according to an embodiment. In this embodiment, power tool 500 mayinclude a motor control circuit 504 having a power unit 506 and acontrol unit 508. Similarly to FIG. 7 previously discussed, control unit508 includes a controller 530, a gate driver 532, a power supplyregulator 534, and a power switch 536. Power unit 506 is disposedbetween AC power supply 512 and the motor 502. Power unit 506 includesbridge rectifier 522 and a bus capacitor 524 to produce a positivewaveform on the DC bus line 525.

In this embodiment, power unit 506 includes two power switchingcircuits: a first switch circuit 526 and a second switch circuit 528.Each of the first and second switching circuits 526 and 528 may IGBTssuitable for high voltage applications, though FETs may be alternativelyused in at least one of the first and second switching circuits 526 and528 in some circumstances. The power terminals of both the first andsecond switching circuits 526 and 528 are coupled to the DC bus line525. The outputs of the first switch circuit 526 are coupled to windingsA-C of the motor 502. The outputs of the second switch circuit 528 arecoupled to windings D-F of the motor 502.

According to an embodiment, windings A-C of the motor 502 are wound in awye configuration, as shown in the exemplary cross-sectional view ofFIG. 37. Windings D-F of motor 502 are wound in a delta configuration,as shown in the cross-sectional view of FIG. 38.

According to an embodiment, controller 530 drives both sets of windingsA-C and D-F via the first and second switch circuits 526 and 528 using asix-phase commutation sequence depicted in the exemplary waveformdiagram of FIG. 39, according to an embodiment. As shown herein, in anembodiment, the drive signals for the second switch circuit 528 (i.e.,the delta converter) include a 30 degree delay compared to the drivesignals for the first switch circuit 526 (i.e., the wye converter). Inother words, the wye connection drive signals are advanced by 30 degreescompared to the delta connection drive signals. This arrangement ensuresthat the motor phase current on the delta windings is properly alignedwith respect to the back-EMF of the motor.

FIG. 40 depicts a waveform diagram showing the motor phase currents forphases A (wye connection) and D (delta connection) using theabove-described circuit, winding arrangement, and commutation sequence,according to an embodiment. FIG. 41 depicts a waveform diagram showingthe motor line current for phases A (wye connection) and D (deltaconnection), showing the 30 degree delay in the delta connection motorline current, according to an embodiment. It is noted that the motorphase currents are the currents flowing through the motor's respectivephase windings, and the motor line currents are measured at the outputterminals of the first and second switch circuits 526 and 528 going intothe motor.

As shown in FIG. 40, due to the presence of two current paths for thephase current in a delta connection, the phase current in a deltaconnection is approximately 180 degrees in each AC half cycle. Bycontrast, the phase current in a wye connection is approximately 120degrees in each AC half cycle. In the delta connection, the phasecurrent in each phase turns positive 60 degrees before the correspondinghigh-side switch turns on. Thus, without the 30 degree delay in thedelta for delta phase currents (i.e., if both the first and secondswitch circuits 526 and 528 were driven using the same drive signals),the delta phase currents (e.g., phase A) would lead the wye phasecurrents (e.g., phase D) by 30 degrees, placing the delta phase out ofalignment with the motor back-EMF. The 30 degree delay ensures that themotor phases are properly aligned with the motor back-EMF. In otherwords, while the shapes of the motor phase currents for the wye anddelta connections are different (i.e., 120 degrees compared to 180degrees in width), with the 30 degree delay, both are properly alignedwith the motor back-EMF, allowing the root-mean-square (RMS) values ofboth phases to be approximately the same.

In an embodiment, the 30 degree delay for the wye connection drivesignals discussed above provides an opportunity to operate the BLDCmotor effectively as a six-phase machine relative to the AC inputcurrent. In other words, while the motor emulates a three-phase machinedue to the alignment of the delta and wye phases, it draws current fromthe power supply in six phases due to the shift in the motor linecurrents of the delta-connected windings, as shown in FIG. 41.

FIG. 42 depicts a waveform diagram showing another comparative view ofthe motor line current for phases A (wye connection) and D (deltaconnection), as well as the AC input current as measured from the powersupply. As shown herein, since the motor line currents for the wye anddelta connections are out of phase as a result of the six-phasecommutation scheme described above, the current draw from the AC powersupply does not drop to zero between the motor commutation switchingsequences. Specifically, in a conventional six-step three-phase, thecurrent flowing into the inverter circuit drops to zero for each of thesix commutation steps between the time one of the switches turns off andthe time the subsequent switch turns on. Thus, the current on the ACline cycle drops to zero within each motor commutation cycle, as shownin FIG. 33. By contrast, using the six-phase commutation sequence ofthis disclosure, as shown in FIG. 39, when one switch of the firstswitch circuit 526 transition turns off, the corresponding switch of thesecond switch circuit 528 remains on for another 30 degrees andcontinues to draw current from the power supply. Thus, the current doesnot drop to zero within each commutation cycle. This drastically reducescurrent transients on the AC line current from the power supply, whichreduces current harmonics.

FIG. 43 depicts comparative waveform diagrams of the AC input currentfor a conventional three-phase motor, e.g., one shown in FIG. 33, andthe AC input current according to the six-phase commutation sequence ofthis disclosure, according to an embodiment. As shown in this figure andFIG. 42, the current fluctuations on the AC input current from the powersupply are substantially less in the present embodiment than the currentspikes for the conventional three-phase motor.

This arrangement reduces the AC input current harmonics frequencies,which is needed to comply with certain regulatory standards. Also, sincethe AC input current waveform has a more sinusoidal shape, thisarrangement significantly improves power factor. As shown in FIG. 44,the above-described embodiment improves power factor from under 0.8 tomore than 0.9 and close to 0.95 in mid torque ranges.

Moreover, as shown in FIG. 46, the above-described embodimentunexpectedly improves system efficiency, by approximately 5-10% in hightorque ranges. Also, as shown in FIG. 45, the above-described embodimentsignificantly improves power output. Although it was originally expectedby the inventor of this disclosure that the wye and delta would behaverelatively independently, it is believed that the magnetic couplingbetween corresponding phases of the delta and wye connections indeedimproves motor power output and system efficiency.

Some of the techniques described herein may be implemented by one ormore computer programs executed by one or more processors residing, forexample on a power tool. The computer programs includeprocessor-executable instructions that are stored on a non-transitorytangible computer readable medium. The computer programs may alsoinclude stored data. Non-limiting examples of the non-transitorytangible computer readable medium are nonvolatile memory, magneticstorage, and optical storage.

Some portions of the above description present the techniques describedherein in terms of algorithms and symbolic representations of operationson information. These algorithmic descriptions and representations arethe means used by those skilled in the data processing arts to mosteffectively convey the substance of their work to others skilled in theart. These operations, while described functionally or logically, areunderstood to be implemented by computer programs. Furthermore, it hasalso proven convenient at times to refer to these arrangements ofoperations as modules or by functional names, without loss ofgenerality.

Unless specifically stated otherwise as apparent from the abovediscussion, it is appreciated that throughout the description,discussions utilizing terms such as “processing” or “computing” or“calculating” or “determining” or “displaying” or the like, refer to theaction and processes of a computer system, or similar electroniccomputing device, that manipulates and transforms data represented asphysical (electronic) quantities within the computer system memories orregisters or other such information storage, transmission or displaydevices.

Certain aspects of the described techniques include process steps andinstructions described herein in the form of an algorithm. It should benoted that the described process steps and instructions could beembodied in software, firmware or hardware, and when embodied insoftware, could be downloaded to reside on and be operated fromdifferent platforms used by real time network operating systems.

The foregoing description of the embodiments has been provided forpurposes of illustration and description. It is not intended to beexhaustive or to limit the disclosure. Individual elements or featuresof a particular embodiment are generally not limited to that particularembodiment, but, where applicable, are interchangeable and can be usedin a selected embodiment, even if not specifically shown or described.The same may also be varied in many ways. Such variations are not to beregarded as a departure from the disclosure, and all such modificationsare intended to be included within the scope of the disclosure.

Example embodiments are provided so that this disclosure will bethorough, and will fully convey the scope to those who are skilled inthe art. Numerous specific details are set forth such as examples ofspecific components, devices, and methods, to provide a thoroughunderstanding of embodiments of the present disclosure. It will beapparent to those skilled in the art that specific details need not beemployed, that example embodiments may be embodied in many differentforms and that neither should be construed to limit the scope of thedisclosure. In some example embodiments, well-known processes,well-known device structures, and well-known technologies are notdescribed in detail.

The terminology used herein is for the purpose of describing particularexample embodiments only and is not intended to be limiting. As usedherein, the singular forms “a,” “an,” and “the” may be intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. The terms “comprises,” “comprising,” “including,” and“having,” are inclusive and therefore specify the presence of statedfeatures, integers, steps, operations, elements, and/or components, butdo not preclude the presence or addition of one or more other features,integers, steps, operations, elements, components, and/or groupsthereof. The method steps, processes, and operations described hereinare not to be construed as necessarily requiring their performance inthe particular order discussed or illustrated, unless specificallyidentified as an order of performance. It is also to be understood thatadditional or alternative steps may be employed.

1. A power tool comprising: an electric brushless direct current (BLDC)motor having a rotor and a stator defining a plurality of phasesassociated with a plurality of windings; a power unit electricallyconnected between a power supply and the motor, the power unit includinga first switch circuit connected electrically to a first set of statorwindings of the plurality of windings and a second switch circuitconnected electrically to a second set of windings of the plurality ofwindings, the first switch circuit and the second switch circuit beingarranged to facilitate one of a series or a parallel connection betweencorresponding windings of the first and second sets of stator windings;and a controller configured to control a switching operation of thefirst switch circuit and the second switch circuit to regulate a supplyof power from the power supply to the motor.
 2. The power tool of claim1, wherein the power supply comprises a direct current (DC) powersupply.
 3. The power tool of claim 1, wherein the power supply comprisesan alternating-current (AC) power supply and a bridge rectifier arrangedto generate a positive voltage waveform from the AC power supply.
 4. Thepower tool of claim 3, further comprising a capacitor coupled to therectifier.
 5. The power tool of claim 1, wherein the first switchcircuit and the second switch circuit both comprise a plurality ofinsulated-gate bipolar transistors (IGBTs) or a plurality offield-effect transistors (FETs).
 6. The power tool of claim 1, whereinthe first switch circuit and the second switch circuit each includes apositive terminal and a negative terminal.
 7. The power tool of claim 6,wherein the positive terminals of the first and second switch circuitsare commonly coupled to a positive terminal of the power supply, and thenegative terminals of the first and second switch circuits are commonlycoupled to a negative terminal of the power supply, to effectivelycreate a parallel connection between corresponding windings of the firstand second sets of stator windings.
 8. The power tool of claim 6,wherein the positive terminal of the first switch circuit and thenegative terminal of the second switch circuit are electrically coupledto the power supply, and the negative terminal of the first switchcircuit is electrically coupled to the positive terminal of the secondswitch circuit, to effectively create a series connection betweencorresponding windings of the first and second sets of stator windings.9. The power tool of claim 8, wherein the first switch circuit and thesecond switch circuit each comprises a plurality of power switcheshaving a voltage rating that is approximately half a nominal voltage ofthe power supply.
 10. The power tool of claim 6, further comprising aswitching unit disposed between two or more of the positive and negativeterminals of the first and second switch circuits to selectively connectthe first switch circuit and the second switch circuit in a way tofacilitate one of a series or a parallel connection betweencorresponding windings of the first and second sets of stator windings.11. The power tool of claim 10, wherein the switching unit selectivelycouples the negative terminal of the first switch circuit to one of thepositive terminal of the second switch circuit or the negative terminalof the second switch circuit.
 12. The power tool of claim 10, whereinthe switching unit comprises two single-pole double-throw switches. 13.The power tool of claim 1, wherein the corresponding windings of thefirst and second sets of stator windings are not electrically connectedvia an electrical connection on the stator.
 14. The power tool of claim1, wherein the controller is configured to control motor commutation byconcurrently driving the first switch circuit and the second switchcircuit using one set of drive signals.